Generally, when making the outer walls 1 of a building such as a house out of mortar walls, water-resistant asphalt-impregnated paper 3 is first attached over the substrate 2 of the building by means of staples 4, lath 5 is attached to that surface by means of staples 4, then undercoat mortar 6 and overcoat mortar 7 are coated in order to finish, as shown in FIG. 4.
In this case, when the overcoat mortar 7 is coated directly after the undercoat mortar 6 has been coated during finishing by coating with the overcoat mortar 7, there is the risk that the undercoat mortar 6 could crumble away under its own weight. Therefore, conventionally, the undercoat mortar 6 is cured to harden, then the surface of the undercoat mortar 6 is rinsed with water before the overcoat mortar 7 is coated for finishing.
However, with the above-mentioned installation procedure, there is a problem in that the installation work can become prolonged since the installation work must be halted for curing after the undercoat mortar 6 has been coated. Furthermore, the addition of more water than is required (surplus water) for a cement hydration reaction to the mortar 6, 7 for the purposes of contributing spreadability to the mortar 6, 7 and increasing the workability during coating also causes prolongation of the curing time.
On the other hand, during the summertime, direct exposure to sunlight of the mortar 6, 7 during curing often causes a dry-out phenomenon wherein the surface of the mortar 6, 7 dries too quickly and forms cracks.
Additionally, when the undercoat mortar 6 is coated onto an asphalt impregnated paper 3, water from the undercoat mortar 6 often moistens the substrate 2 by seeping through the holes of the staples 4, therefore running the risk of causing corrosion or the like.
Furthermore, there is the problem that the asphalt impregnated paper 3 is low in strength, so that it is easily torn during the installation work and can result in the generation of cracks in the outer wall 1 after installation, or make the mortar more prone to crumbling due to earthquakes or the like.